Currently, high purity Ti is used extensively in the fabrication of microprocessors and similar components for the microelectronics industry. Constantly evolving microprocessor capabilities (increasing integration, decreasing circuit element dimensions) have driven producers to meet the demands of chip manufacturers for increasingly pure titanium.
High purity Ti targets are used in sputtering applications to produce thin films on microprocessors, integrated circuits, DRAMs, flat panel displays, etc. Purity requirements range from 99.99% (4N) to 99.99999% (7N), depending on the application. For improved end usage properties, it is of interest to decrease impurity elements including, but not limited to, alkali metals such as Na and K, heavy metals such as Fe, Ni and Cr, radio active elements such as U and Th and gases, especially oxygen. These elements have undesirable affects on properties; for example, Fe contamination degrades film patterning and circuit element registry, oxygen affects the resistivity of the deposited film; Na and K migrate from deposited films into active transistor elements thus degrading performance, and U and Th are both alpha-emitters which can cause adjacent solid state switches to change state. So called "6N" purity Ti, where total impurities (excluding gases) are less than 1 ppm, and with low oxygen, ea. &lt;100 ppm, is presently desired in the industry for many of the above applications. Lowering the amounts of impurity elements can improve the performance of the sputtering process and increase the reliability and speed of the microprocessor or memory device in which the high purity titanium is used.
Common processes for producing high purity titanium include: (1) producing Ti sponge by reacting TiCl.sub.4 with a reducing agent such as Mg or Na in a vessel designed for this purpose, (2) vacuum distilling Ti sponge in a vacuum distilling apparatus to remove residual salt or otherwise treat sponge to remove residual salt, (3) electrolyze Ti sponge in an electrolytic cell by fused salt electrolysis, and (4) melting Ti using an electron-beam furnace or similar high-vacuum melting process. Titanium sputtering targets may be produced from ingot produced by a combination of these processes.